Field of the Invention
The present invention relates to an acoustic wave device, and more specifically, to an acoustic wave device which can guarantee a pressure resistance characteristic and improve reliability.
Background of the Related Art
A Wafer Level Package (WLP) process may manufacture a package as a complete product at a wafer level, i.e., while individual chips are not isolated from a wafer. Existing facilities and processes may be used as they are in a manufacturing facility and a manufacturing process used for manufacturing the package. Since such a WLP process proceeds a packaging process in a wafer state, hundreds and thousands of packages can be produced in a single packaging process, and thus manufacturing cost can be greatly reduced compared with an existing method which proceeds the packaging process by the unit of individual chips.
Recently, the wafer level packaging technique described above is also applied to fabricate a small and thin surface acoustic wave (SAW) filter. Since a SAW filter package operates as a filter by arranging an IDT in a cavity created by a substrate, a side wall and a cover and using mechanical vibration of the IDT, the cavity should be perfectly protected. However, the process of manufacturing an electronic device including a SAW filter produced in the WLP method has a problem particularly incapable of sufficiently enduring the high pressure of a transfer molding process.
Although the side wall and the cover are formed using a strong material the same as that of the substrate in some cases in order to improve the problem, there is a problem of high manufacturing cost and low throughput.
U.S. Pat. No. 8,436,514 described below is for improving the problems described above, and FIG. 1 is the representative figure of the prior art and a cross-sectional view showing the structure described in the prior art, and FIG. 2 is FIG. 1A of the prior art, which is a plan view showing the structure described in the prior art. The prior art describes to endure the pressure of the transfer molding process by adding a conductive layer (18 of FIG. 1) on a protective cover (7 of FIG. 1). Particularly, referring to FIG. 2, the prior art describes to effectively endure the pressure by forming the conductive layer wide on the top surface of an acoustic wave device, and claim 13 of the prior art specifies to form an area of the conductive layer as wide as more than 50% of the area of the top surface of the acoustic wave device.
However, the method of the prior art generates another problem. When the conductive layer is formed wide on the top of the protective cover, a phenomenon (warpage) of bending the substrate of the acoustic wave device occurs. When the substrate is formed thick to prevent such a phenomenon, it is moving against the trend of thinning the acoustic wave device, and when the substrate is ground after the WLP is performed on the thick substrate, manufacturing cost increases and throughput is lowered due to additional processes.
When an acoustic wave device is formed, a single crystal material such as LiTa2O3 is frequently used as a substrate, and such a material is disadvantageous in that it is easily broken by a physical shock applied from outside. Accordingly, it should be handled with care in the manufacturing process. More problems are raised as bending the substrate increases.
For example, when a laminating process or a coating process is applied to form an insulation cover layer after forming a conductive layer, the substrate is put on a vacuum chuck and flattened using vacuum. However, there is a problem in that a substrate with the warpage described above is easily broken in this process or a material for forming the insulation cover layer is not uniformly applied on the substrate. Furthermore, even in a process of separating (sawing) a plurality of acoustic wave devices manufactured in a state of a wafer in the WLP manufacturing process into individual acoustic wave devices, a problem of easily breaking the substrate occurs.